Observing the prompt emission of GRBs

Abstract

Gamma-ray bursts (GRBs) were first detected thanks to their prompt emission, which was the only information available for decades. In 2010, while the high-energy prompt emission remains the main tool for the detection and the first localization of GRB sources, our understanding of this crucial phase of GRBs has made great progress. We discuss some recent advances in this field, like the occasional detection of the prompt emission at all wavelengths, from optical to GeV; the existence of sub-luminous GRBs; the attempts to standardize GRBs; and the possible detection of polarization in two very bright GRBs. Despite these advances, tantalizing observational and theoretical challenges still exist, concerning the detection of the faintest GRBs, the panchromatic observation of GRBs from their very beginning, the origin of the prompt emission, or the understanding of the physics at work during this phase.Significant progress on this last topic is expected with SVOM thanks to the observation of dozens of GRBs from optical to MeV during the burst itself, and the measure of the redshift for the majority of them. SVOM will also change our view of the prompt GRB phase in another way. Within a few years, the sensitivity of sky surveys at optical and radio frequencies, and outside the electromagnetic domain in gravitational waves or neutrinos, will allow them to detect several new types of transient signals, and SVOM will be uniquely suited to identify which of these transients are associated with GRBs. This radically novel look at GRBs may elucidate the complex physics producing these bright flashes.

Plasmas in Gamma-Ray Bursts: Particle Acceleration, Magnetic Fields, Radiative Processes and Environments

“…I should stress that I limit the discussion here to plasma physics phenomena only; in recent years, there have been many excellent reviews covering various aspects of GRB phenomenology and physics, and I refer to reader to these reviews for a more comprehensive discussion on the various subjects. A partial list includes Atteia and Boër [12], Gehrels and Mészáros [13], Bucciantini [14], Gehrels and Razzaque [15], Daigne [16], Zhang [17], Berger [18], Meszaros and Rees [19], Pe'er [20], Kumar and Zhang [21], Granot et al [22], Zhang et al [23], Toma et al [24], Pe'er and Ryde [25], Beloborodov and Mészáros [26], Dai et al [27], van Eerten [28], Nagataki [29].…”

Toward Early-Warning Detection of Gravitational Waves From Compact Binary Coalescence

“…The prompt emission is a probe into the extreme initial conditions of the outflow, in contrast with afterglows, which arise in the external shock with the local medium and are relatively insensitive to initial conditions. Optical flashes have been observed for a handful of long GRBs (Atteia & Boër 2011) by telescopes with extremely rapid response or, in the case of GRB 080319b, by pure serendipity, where several telescopes were already observing the afterglow of another GRB in the same field of view (FOV; Racusin et al 2008). The observed optical flashes peaked within tens of seconds and decayed quickly.…”

GRB 090727 and Gamma-Ray Bursts With Early-Time Optical Emission

“…Despite the growing number of gamma-ray light curves obtained to date, the rich variety in temporal and spectral properties coupled with the challenge in obtaining panchromatic observations simultaneously with prompt gamma-ray emission has limited understanding of the underlying physical processes. Although the variability in GRB light curves suggests internal dissipation processes for prompt gamma-ray emission, fundamental theoretical questions remain on the actual dissipation mechanism, the presence of thermal components and the role of magnetic fields (e.g., Atteia & Boër 2011;Harrison & Kobayashi 2013 The first detection of optical emission during the prompt gamma-ray phase was made for GRB 990123 (Akerlof et al 1999), which stimulated research efforts on theoretical and observational side. The launch of NASA's Swift satellite (Gehrels et al 2004) revolutionised the study of GRBs and opened a new window on the very early time properties of GRBs; in particular, the real-time dissemination of accurate (3 arcmin error circles) gamma-ray positions from its Burst Alert Telescope (BAT) via the Gamma-ray Coordinates Network (GCN) (Barthelmy et al 1994), are key for driving rapid-response ground-based observations from fully autonomous robotic optical/IR telescopes such as the 2-m Liverpool Telescope -LT (Steele et al 2004;Guidorzi et al 2006).…”